Fluid directing member



May 26, 1959 E. G. PEKAREK FLUID DIRECTING MEMBER Filed May 24, 1956 2Sheets-Sheet 2 REDUCTION United States Patent() FLUID DIRECTING MEMBEREdward vG. Pekarek, Willoughby, Ohio, assignor to Thompson RamoWooldridge, Inc., a corporation of Ohio Application May 24, 1956, SerialNo. 586,995

5 Claims. (Cl. 253--77) The present invention relates to improvements influid directing members and, in particular, deals with improvements inparts adapted for use in jet engines.

In the manufacture of parts such as turbine buckets, compressor blades,nozzle diaphragm vanes and the like, there is presented the problem ofproviding a complex shape to within very close tolerances. Coupled withthis requirement is the necessity of employing a strong, creep resistantmetal or alloy for the body of the element which is capable ofwithstanding a combination of complex, superimposed thermal fatigue andbending stresses. In many cases, suitable metals or alloys due to theirrefractory nature cannot be adapted to convention-al forging practiceswithout considerable difficulty, or they may require the employment ofinvestment casting procedures to permit their fabrication-into usefulparts. Even with these modifications, however, the number of rejects washigh and the processes were accordingly quite expen-sive.

The present invention overcomes these difliculties and provides a fluiddirecting member composed of an integral casting with portions thereofbeing selectively treated to permit those portions to resist moreadequately the types of stresses to which they are subjected duringoperation.

An object of the present invention is to provide an improved uiddirecting member which can be shaped by conventional hot-workingprocedures.

Another object of the invention is to provide a fluid directing memberof the turbine blade type from an integral casting, with localizedareas' of said uid directing member being treated to provide in themember localized areas capable of more adequately resisting theparticular types of stresses to which those areas are subjected duringoperation.

Another object of the, present invention` is to provide a fluiddirecting member from alloys in the as cast condition, with selectedportions thereof being .in a wrought condition.

The fluid directing member of the present invention is particularlyadapted to use in conditions of high temperatures and extreme stresses,such as exist in the operation of a jet turbine engine. Such fluiddirecting'members may, for example, take theform of turbine buckets,compressor blades and nozzle diaphragm vanes each of which must becapable of resisting corrosion, and each of which has its owncombination of working stresses which must be resisted adequately at theoperating temperatures employed. A turbine bucket, for example, issubjected during use to various types of stresses. The turbine lbucketis subjected to creep stresses `in the root area of the bucket duringoperation due to the effects of centrifugal force. At the same time, thetip end of the vane, and the leading and trailing edges of the turbinebucket are subjected to fatigue stresses occasioned by vibration andthermal stresses due to rapid changes in temperature along the edges. Inorder to resist the stresses adequately,

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relatively ductile preform. This preform is made somewhat oversize inselected degrees, so that after a subsequenlt working operation, such ascoining, the finished part has the correct dimensions and the areas inwhich the excess metal appears in the preform are transformed into aWrought condition which is better able to resist fatigue stresses andthermal stresses. g

The present invention may employ alloys which have heretofore been oflimited utility in this field' because of the difficulty of forging suchalloys from bar stock or ingot form. Particularly good results have beenobtained with nickel base, precipitation hardenable alloys containingfrom about 13 to 21% chromium, from 1.0 to 6.0% molybdenum, from 1.0 to4.0% aluminum, from 1.5 to 3.5% titanium, a maximum of about 0.2%carbon, and in some cases, from about 10 to 35% cobalt, with the balancebeing substantially nickel. A particularly preferred alloy has thefollowing composition:

C 0.1 to 0.2% by weight. Mn 0.25maximum.

Si 0.60 maximum.

Cr 14 to 17%.

Mo 4.5 to 6.0%.

Ti 1.5 to 2.5%.

Al i2.5 to 3.5%.

B .025 to .07%.

Fe 8 to 12%.

Ni Substantially the balance.

Another suitable alloy is that known commercially as Waspaloy having thefollowing analysis:

C 0.1 maximum. f

Cr 18.0 to 21.0%.

Co 12.0 to 15.0%.

Mo l3.5 to 5.0%.

Al 1.0 to 1.5%.

Ti 2.75 to 3.25%.

Ni Substantially the balance.

The originalI casting is made under vacuum conditions in order to securegreater high temperature strength and the metallurgical properties ofthe bucket, according to n a higher degree of ductilityin the casting.In making the casting, pressures on the order of less than onemillimeter of mercury and preferably not in excess of about micronsofmercury are appropriate. Satisfactory results can also be obtained byremelltin'g a master melt previously made under vacuum conditions in aninert atmosphere. 1

The casting which results, particularly if cooled relatively slowly,is'likely to exhibit a coarse crystalline structure characterized by thepresence of dendrites. One of the features of the present inventionresides in maintaining the as-cast structure in portions of the uiddirecting member, particularly in the relatively massive root portion ofa turbine blade and in the airfoil area adjacent fto the root.Tests'have indicated, for example, that the as-cast condition provides abetter resistance to oreep stresses than does a relatively finecrystalline structure typical of a hot-worked alloy composition.

A further description of the present invention will be made inconjunction with the attached sheets of drawings which'illustrate theimproved article of the present invention and a method for itspreparation.

On the drawings:

Figure l is a cross sectional view of a preform used in the manufactureof a turbine bucket according to the present invention;

Figure 2 is a greatly enlarged cross sectional view of the vane portionof the preform, illustrating its crystalline structure;

Figure 3 is a view similar to Fig. 1, but illustrating the grainstructure of the tunbine 'bucket after portions of the bucket have beenconverted to a wrought condition;

Figure 4 is a view similar to Fig. 2 illustrating the crystal structureof the vane portion existing in the turbine bucket of Fig. 3;

Figure 5 is a view in elevation of the completed turbine bucket;

Figure 6 is a view in elevation of a preform having a aw therein;

Figure 7 is a greatly enlarged fragmentary view taken substantiallyalong the line VII-VH of Fig. 6 to illustrate the iiaws;

Figure 8 is a view similar to Fig. 7 but illustrates the condition ofthe preform after the flaw has `been ground down;

Figure 9 is a view like Fig. 7 except that it illustrates the area ofthe iiaw after the working operation; and

Figure 10 is a graph illustrating the effect that the amount ofreduction has upon the stress rupture life of the alloy samples.

As shown on the drawings:

In Fig. l, reference numeral 10 indicates generally a preform for themanufacture of a shrouded turbine bucket which includes a relativelymassive base or root portion 11, an arcuate twisted vane portion 12 anda relatively thin shroud 13. As seen in both Figs. l and 2, the preform10 is in the as cast condition, having been produced either by meltingunder vacuum conditions, or by remelting a master melt from a vacuummelting under inert conditions. If the preform is cooled slowly as inconventional investment casting practice, the metallurgical structurethereof will be characterized lby a large number of coarse graineddendrites 14 as illustrated in Figs. 1 and 2.

As shown in Fig. 2, the van portion 12 of the preform 10 is madeoversize, the amount of oversizing rbeing greatest, as indicated by thedashed line which defines the ultimate shape of the Vane portion, at theleading edge 12a and the trailing edge 12b of the preform 10. The excessmetal at these portions is provided so that subsequent hot working ofthe metal will be effective to reduce the oversize areas of the preform10 to the desired dimensions and simultaneously provide a wroughtcondition in those areas of the turbine bucket.

As illustrated in Figs. 3 and 4, the preform 10 after hot working, suchas by a coining operation, is converted to the finished turbine bucket16 having a relatively massive root portion 17, an arcuate, contouredvane portion 18 and a shroud 19. The areas adjacent the leading edge18a, the trailing edge 18h, and the area immediately below the shroud19, designated by 18e (Fig. 5) are all worked to the extent of providinga wrought structure in those portions of the bucket. The dashed linelabeled 20 in Fig. 5 outlines the worked areas on the vane portion.

As best illustrated in Figs. 3 and 4, the `wrought structure ischaracterized by a large number of relatively small grains 21 in theworked areas, leaving the dendrites 14 centrally of the tur-bine bucket(and also in the root portion 17). With this type of structure, theportions of the bucket which are most likely to be subjected to fatiguestresses contain the fine grained structure while those portions of thebucket which must resist centrifugal forces tending to produce creepstresses remain in the as cast condition in which the crystalline formis relatively coarse.

The temperature of hot working may vary considerably, depending upon thecomposition, but ordinarily temper- 4 atures on the order of about 1950to 2l50 F. are appropriate for nickel base alloys.

One of the advantages of providing an oversized preform according to theprocess described is the ability to correct minor surface defects in theturbine bucket during the final hot working operation. Ordinarily, minorsurface defects maybe tolerated in the central portion of the vane butnot in the portions of the bucket adjacent the leading and trailingedges, and adjacent the shroud or root. The inner outline of thesecritical areas has been designated in Fig. 6 of the drawings by thedashed line labeled Z2.

Such surface defects are most likely to occur in the relatively thinleading edge or trailing edge portions and one such defect, identifiedat numeral 23, has been indicated in Figs. 6 and 7 of the drawings. Toeliminate this defect, the flaw 23 is ground down to produce arelatively shallow depression 24 as illustrated in Fig. 8 of thedrawings and then the preform 10 is subjected to the coining operation.The flow of metal which results during the coining operation due to theexcess of metal located in the areas of the leading edge 12a fills upthe void created by the depression 24 and creates a substantially smoothcontour as indicated at numeral 26 in Fig. 9. The ow of metal duringcoining also produces a flash 27 which can easily be trimmed off thecoined article. The dotted line 28 in Fig. 9 indicates the originaldimensions of the preform.

The substantial improvement in stress rupture life of an as castspecimen as compared to a wrought specimen is best illustrated in thegraph of Fig. l0. After a reduction of about 30%, the stress rupturelife of the sample alloy levels off at about 10() hours, whereas in theunreduced or as cast condition, the stress rupture life of the samealloy was in the neighborhood of 400 hours. These differences in stressrupture life are directly related to the ability of the alloy to resistcreep at elevated temperatures. On the other hand, it has beendemonstrated that fine grained wrought material has greater fatiguestrength than large grained castings.

From the foregoing, it will be evident that the fluid directing memberof the present invention provides a single integral structure withlocalized areas particularly adapted to resist those stresses Iwhichthey encounter in normal operation. It will also -be evident thatvarious modifications can be made to the described embodiments withoutdeparting from the scope of the present invention.

I claim as my invention:

1. A fluid directing member subject to creep stresses and fatiguestresses during use comprising a relatively massive root portion and arelatively thin vane portion, said root portion and said vane portionbeing composed of an integral metal casting, said root portion beingcharacterized by a relatively coarse crystalline structure, and theleading and trailing edges of said vane being characterized by arelatively ii-ne grained crystalline structure.

2. A liuid directing member comprising a lrelatively massive rootportion and a relatively thin vane portion, said root portion and saidvane portion being composed of an integral metal casting, said rootportion being characterized by a relatively coarse crystalline structureincluding dendrites and the leading and trailing edges of said vanebeing characterized by a relatively fine grained crystalline structure.

3. A fluid directing member subject to creep stresses and fatiguestresses during use comprising a relatively massive root portion and arelatively thin vane portion, said root portion and said vane portionbeing composed of an integral metal casting consisting essentially of anickel base precipitation hardenable alloy, said root portion beingcharacterized by a relatively coarse crystalline structure, and theleading and trailing edges of said vane asses 5 being characterized by arelatively line grained crystalline structure.

4. A fluid directing member subject to creep stresses and fatiguestresses during use comprising a relatively massive root portion, arelatively thin vane portion, and an outwardly flared shroud, said rootportion and said vane portion being composed of an integral metalcasting, said root portion and said shroud being characterized by arelatively coarse crystalline structure, and said vane portion having aleading edge and a trailing edge, both characterized by a relatively negrained crystalline structure.

5. A turbine bucket comprising a relatively massive root portion and arelatively thin vane portion, said root portion and said vane portionbeing composed of an inte gral metal casting, said root portion beingcharacterized by arelatively coarse crystalline structure and theairfoil edges of said vane being characterized by a Irelatively inegrained crystalline structure.

References Cited in the le of this patent UNITED STATES PATENTS1,294,732 Weber f Feb. 18, 1919 1,493,211 Link May 6, 1924 1,670,345Comte May 22, 1928 1,837,439 Holzwarth Dec. 22, 1931 2,382,273Thielemann Aug. 14, 1945 FOREIGN PATENTS 2,241 Great Britain 1880

